1. Field of the Invention
This invention relates to an apparatus for measuring the characteristics of an optical system such as spherical power, cylindrical power, cylindrical axis, prism power and prism axis, and more particularly to a so-called automatic lens meter for automatically measuring chiefly the refractive characteristic of spectacle lenses.
2. Description of the Prior Art
As far as automatic lens meters are concerned, various measuring methods have heretofore been proposed. Among these, a method generally proposed in recent years comprises causing a parallel light beam to enter a lens to be examined, photoelectrically detecting the inclination of the beam passed through the lens to be examined and bent by the refractive characteristic thereof, and calculating the refractive characteristic of the lens to be examined from such inclination. Various contrivances have been made in the detection of the inclination of the beam and the method of processing thereof and there are the following prior arts:
(1) Japanese Laid-open Patent Application No. 449/1977 (corresponding U.S. Pat. No. 4,007,990);
(2) Japanese Laid-open Patent Application No. 14757/1979 (corresponding U.S. Pat. No. 4,180,325);
(3) Japanese Laid-open Patent Application No. 86327/1981 (corresponding U.S. application Ser. No. 85864 filed on Oct. 18, 1979);
(4) Japanese Laid-open Patent Application No. 168140/1981 (corresponding German Patent Application No. 2934263); and
(5) Japanese Laid-open Patent Application No. 29923/1982.
The problems peculiar to these prior art will hereinafter be pointed out.
In prior art (1), a projected light beam and a one-dimensional position sensing detector must be rotated in synchronism with each other and, where there is a prism power in a lens to be examined, a mechanical apparatus for compensating for this is necessary, and this leads to a complex construction and difficulty in the manufacture thereof.
In prior art (2), the number of projected light beams used for measurement is small and therefore, very high accuracy is required for the detection of the inclinations of the beams and this leads to difficulties in the manufacture and adjustment or otherwise, it is impossible to maintain the measurement accuracy high.
In prior art (3), it is necessary to rotate a linear photodiode array which is an electrical part and this leads to a problem in the manufacture. Also, where there is a prism power in the lens to be examined, calculation becomes complicated and a long processing time of the processor is required, and this is disadvantageous for quick measurement.
In prior art (4), where there is a cylindrical power in the lens to be examined, a mechanical apparatus for rotating a diode array to thereby correct the cylindrical axis is required and further, where there is a prism power in the lens to be examined, a mechanical apparatus for compensating for this is also required and thus, the construction must unavoidably be complicated to make the measuring apparatus more perfect.
In prior art (5), it is difficult to obtain a two-dimensional sensor having a sufficient resolving power and this leads a problem in the manufacture. Also, to calculate a result by using the output signal from the two-dimensional sensor, complicated calculation is necessary and this undesirably leads to complication of the operational device and lengthened processing time.